S. Vercellone, et al. (incl. M. Böttcher,
P. Roustazadeh, and N. Palma),
Astrophysical Journal, submitted (2009)
We report on eighteen months of multiwavelength observations of the blazar 3C454.3 (Crazy Diamond) carried out in the period July 2007 - January 2009. In particular, we show the results of the AGILE campaigns which took place on May - June 2008, July - August 2008, and October 2008 - January 2009. During the May 2008 - January 2009 period, the source average flux was highly variable, with a clear fading trend towards the end of the period, from an average gamma-ray flux FE > 100 MeV > 200 X 10-8 photons cm-2 s-1 in May - June 2008, to FE > 100 MeV ~ 80 X 10-8 photons cm-2 s-1 in October 2008 - January 2009. The average gamma-ray spectrum between 100 MeV and 1 GeV can be fit by a simple power law, showing a moderate softening (from GammaGRID ~ 2.0 to GammaGRID ~ 2.2) towards the end of the observing campaign. Only 3 sigma upper limits can be derived in the 20 - 60 keV energy band with Super-AGILE, because the source was considerably off-axis during the whole time period.
In July - August 2007 and May - June 2008, 3C454.3 was monitored by RXTE in the 3 - 20 keV energy band. The RXTE/PCA light curve shows variability in the hard X-ray energy band, correlated with the gamma-ray one. The RXTE average flux during the two time periods is F3 - 20 keV = 9.5 X 10-3 photons cm-2 s-1 and F3 - 20 keV = 5.1 X 10-3 photons cm-2 s-1, respectively, while the spectrum ( a power-law with photon index 1.65 +/- 0.02) does not show any significant variability.
We also carried out simultaneous Swift observations during all AGILE campaigns. Swift/XRT detected 3C454.3 with an observed flux in the 2 - 10 keV energy band in the range (0.9 - 7.5) X 10-11 erg cm-2 s-1 and a photon index in the range 1.33 - 2.04. In the 15 - 150 keV energy band, when detected the source has an average flux of about 5 mCrab.
GASP-WEBT monitored 3C454.3 during the whole 2007 - 2008 period in the radio, millimeter, near-IR, and optical bands. The observations show an extremely variable behavior at all frequencies, with flux peaks almost simultaneous with those at higher energies. A correlation analysis between the optical and the gamma-ray fluxes shows that the gamma - optical correlation occurs with a time lag of -0.4+0.6-0.8 days, consistent with previous findings for this source.
An analysis of 15 GHz and 43 GHz VLBI core radio flux observations in the period 2007 July - 2009 February shows an increasing trend of the core radio flux, anti-correlated with the higher-frequency data, allowing us to derive the value of the source magnetic field.
Finally, the modeling of the broad-band spectral energy distributions (SEDs) for the still unpublished data, and the behavior of the long-term light curves in different energy bands, allow us to compare the jet properties during different emission states, and to study the geometrical properties of the jet on a time-span longer than one year.